Carrier controlled radio receiver



March 13, 1945 R. l. HOLLINGSWORTH 2,371,392 'l CARRIER CONTROL'JJRD RADIO RECEIVER Filed Aprilfls, '1942 OSC/L LA TOI? oc/IL wooonoo "TTORNEY Poieniod'Mar. 13, 1945 CARRiER oorrrRonLEny Ramo RECEIVER R Lee Hollingsworth, Riverhead', N. Y., assignor to l Radio Corporation Delaware of America, a corporation of Application April 1s, 1942', serial No. 439,480 `9 claims. (o1. 25o-2 0) My present invention vrelates to radio receiver. control circuits, and `more particularly to carriercontrolled receiver circuits.

One of the principal objects of my present infY vention .is to'provide a novelmethod of, and meansfor, controlling the output volume of.a radio receiver; the method comprising the steps of rectifying receivedV carrier. energy, and utilizv ing the rectified carrier voltage to control the alternating current `supply rectifierA thereby to regulate the plate supply voltage as a function of carrier intensity. o Q Another important object of my invention is to provide in a receiver a means for com-pensating for carrier fading; for controlling the modue lation level in theaudio amplifier when the cartector; it is assumed the receiver is of the superheterodyne-type, Such a mixer lstage may ernploy a Vpentagrid converter tube of the V6A? type.

The tunable input circuit v3 is coupled -to theqout-a put circuit of am'pliiier 2; ythe rst, or signal -in-` put, grid is connected to input circuit 3'.- j i if Local oscillations, of a frequency differing from. the selected signal frequency yby a predetermined intermediate frequency (I. FJ, are produced at4 `il. The oscillations thereof may be applied-to the oscillator grid, as schematically represented,-

rier fades; for inter-station kmuting and` partial muting on deep selective fading; and for increasing the amplier'grid bias asr the plate voltage is ,still further increased on carrier fading there- -by lguarding against distortion due to-overloading. e

'Another object of my invention is to provide a system for securing automatic gaincontrol and automatic frequency control in a radio receiver; \the control actionsl being secured as a result o f voltage changes on the grid and plates ofthe predemodulator stages as pa function of carrier strength.

Still other objects are to improve generally the efliciency of automatic gain control circuits for receivers, and more especially to provide such circuits in a reliable, economical and readily-manufacturable manner. l

VThe novel features which I believe to be -cha1 acte'ristic of my invention are :set'forthfwithparticularity in the appended claims; the invention itself, however, as to both its organization and method o f operation will best be understood yby referencevto the following description taken in connection lwith the drawing in which. I have' in- 1 dicated -diagraimmatically a circuit organization whereby'myinvention may be carried into effect. Referring, now, to the accompanyingidrawing, letjtbe assumed that the-receiver shownA is gen- '2'. "The following stage i3 isa'mixer, or first de.-

so as to produce the I. F. signal energy'inthey resonant primary circuit of 1.1i.` transforment.4

'I'he oscillator 3" may include any desired type of tube, such as a triode. In such a case, let-it be assumed that the tunable oscillation circuiti is connected between control grid and cathode, While the plate is connected by feedback voltage supply lead 20.

T-he plate supply lead is additionally 'conL nected to the plates of each of amplifier 2and mixer vtube 3. Of course, one or more I. F. amplifiers may follow the I. F. transformery 4'. i The plates of such yamplifiers would `be fed from the line 20. The demodulator, or second detector; consists of tube 5. The latter may be atriode coil 3U to plate 'whose anode and grounded cathode function' as a diode. rectifier. The anode of tube 5 is' connected to the high side of the-I. F.tuned vinput circuit 4'. The -load resistor .6 develops the modu' lati-on signal voltage from the rectilied I. li'.v current. .The resistor `l may bev bypassed-for currents. The slider -6 may derive any magnitude of signal voltage from load 6. The switch arm 8 may be adjusted to position Tito carry a portion of `the voltage to a vdesirable telegraph termination, which -is usuallyy ai tone keyer:- If it is desired to feed'the signal voltage to an audio amplifier (not shown), adjusted to position `8.

-The unidirectional voltage across resistorf is' proportionalin magnitude to the 'carrier intensityi The carrier-derived unidirectional voltage is? applied .overline yHl to the input circuits of the am7 plier 2 and mixer 3. The vletters AVC'indi:-" cate that the line is the automaticvolume, Yor gain, control connection. Appropriate filter net'-` work l1-|8 is inserted in theAVC connection, and provides a proper time delay action. Filter resistors I9 may, also, be inserted inthe ccnl vnections to the signal grid circuits. The AVC'.l

then switch arm t is y with alternating current, say, at 60 cycles. The secondary has two sections. Power rectiiiers I and ,II have the anodes thereof connected to opposite ends of secondary section I2. The section I2 supplies heating current to the filaments of the rectiiiers I0 and Il.

Each rectifier is provided with` a control grid. Thus, grid I0' is positioned between the plate and filament of tube I0, while grid II' acts to control the electron stream in the rectifier II. The midpoint of section I2' is connected through the series inductances of filter I3 to the negative end of the power supply potentiometer. Thel latter consists of resistor sections I4 `and I5; the junction of the latter is grounded. The filter I3 comprises parallel condensers, and lead I5 connects the midpoint of section I2" to the positive end of potentiometer resistor I5. The lead 2li is connected to a desired voltage point on resistor I5 so as to energize the plates of tubes?, 3 and 3" properly.

AVC bias .is applied to the grids IIJ' and I I' of power rectii'iers I0 and II. This is done by connecting both control vgrids to any desired point on resistor 6; the lead 9 may be considered an extension of the AVC circuit. The path including resistor I6 connects the signal grids to a point on potentiometer section I4 which is at a proper negative potential. Resistors I6, I'I and condenser I8 provide a time delay circuit in the AVC connection. Switch 2I may connect the control grid of tube 5 to the AVC circuit, or to the plate of'the demodulator. In the latter case, the tube ing, may be made even more positive by adding this negative control voltage to the grid of tube 5, or another tube that might be selected for this purpose.

Thus, a system has been shown for compensating for carrier fading; for controlling the volume (partially) of the modulation level in the audio amplifier when the carrier fades; formuting between stations and partial muting on deep selective fading; and for increasing the grid bias as the plate voltage is still further increased on cari'ier fading, therebyv guarding against distortion due to overloading.

Another feature in this circuit is the inherent automatic frequency control (AFC) that is possible as a function of the carrier strength. Most oscillators are subject to variation .in frequency as the plate voltage is raised or lowered. Therefore, in such a circuit as I have described, in which both the plate and grid voltages vary as a function of carrier strength, this element of control may be used to cause the local oscillator to center itself, or rather its resultant output, 'through the I. F. amplifier, just as the receiver linearizes 5 functions as a diode without AVC voltage ap-y plied to its grid.

Considering, now, the operation of the system, assume that no modulated carrier waves are beine received. In that case the voltage across resistor 6 is zero, and the rectifier control grids I0 and I I have minimum bias. Hence, the voltage across resistor I4, the signal grid biasing source, is a maximum. As a result, the negative bias on all grids is set at a predetermined value; and the gain of each stage is materially decreased. Concurrently, the drop across plate supply resistor I5 increases, and tends to increase the plate voltage of the controlled tubes. If switch 2l is thrown to contact 2|', the grid of demodulator 5 is biased to secure muting action. When switch 2 I--2I`I is closed,'the effect is to further isolate the radio frequency section from the audio section during no-signal state. When rectified carrier current passes through load resistor 6, the voltages across resistors I4 and I5 are reduced. At first the gain of the receiver is caused to rise by this reduction. When the signal voltage across resistor 6 is the dominant factor of control, the gain of the system is reduced. y

When modulated carrier waves of suilicient in'- tensity are received, the gain is linearized by the increasing bias developed across resistor 6. The rectifier grids I0' and II being biased negatively cause the plate voltages to the various plates to be reduced. Furthermore, the AVC bias applied over lead 'I9 to the signal grids aids in control over the gain of the system. The reduction of plate voltage and increase of AVC bias are such that the carrier amplitude at the input circuit 4' is substantially uniform over a wide range of carrier variation at signal collector I. It is intended that the increase in plate voltage on fading should be enough over that of the grid voltage rise to increase the gain of the receiver. Hence, muting for quiet tuning between stations, and for controlling blasting during selective fadits gain, but only in one tuning direction since this action reduces the capacity across the tuned oscillator circuit through the medium of the oscillator tube.

It is practical to employ ASEC in a receiver even though it is effective only through a capacity change. Tuning to a lower frequency would re-l quire manual tuning slightly beyond the desired station frequency to set the oscillator and radio frequencyin the automatic range. This overswing of the tuning dial is usually a natural tend'- ency. Tuning from a lower to a higher 'frequency would cause the AFC to tune the station in automatically as it is approached by manual tuning. That the radio frequency circuits tune, as va re'V sult of increased plate and grid AVC, is obvious. Therefore, the system of AVC as herein described. with its ability to swing the oscillator and radio frequency amplifier tuning to a certain extent, is practical due tothe amount of AVC available 7 to both the plate and grid circuitsof the tubes controlled.

This method of AFC is most effective when receiving high frequency signals, as for instance frequency modulated carriersignals (FM) of comparatively narrow modulation band width, inv that it compensates for frequency changes in the receiver due to temperature-changes. Also, this method of AFC is most desirable when receiving high frequency signals of the amplitude variety within the primary or non-fading area; looking to the possibility of sky wave suppression for local broadcast usage of certain high frequency bands so that every small newspaper 'could' afford a local station.

While I have indicated and described a system for carrying my invention into eiiect, it willbe apparent to one skilled in the art thatmy invention is by no means limited to the particular organization shown and described, but that many modications may be made without departing from the scope of my invention, as set forth in the appended claims. What I claim is: 1. A method of controlling the gain of a signal amplifier tube provided vwith at least a cathode, signal control electrode and a signal output electrode, which includes the steps of applying signals to the control electrode, 'rectifying -low frequency alternating current to provide energizing voltage for at least said output electrode, rectifying said signals to provide a control voltage, and automatically controlling said alternating current rectication with said control voltage thereby to vary the amplier gain.

2. A method of controlling the gain .of a signal amplifier tube provided with at least a cathode, signal control electrode and a signal output electrode, which includes the steps of applying sig.- nals to the control electrode, rectifying low frequency alternating current to provide energizing voltage for at least said output electrode, providing biasing voltage for said control electrodefrom the rectier alternating current, rectifying said signals to provide a controlvoltage, and automatically controlling said alternating current recalternating current to provide a positive direct tication with said control voltage thereby to vary the amplifier gain.

3. A method of controlling the gain of a signal amplier tube provided with at least a cathode,

and automatically controlling said alternating i current rectiiication with said control voltage thereby to vary the amplifier gain, and concurrently controlling the voltage of said control electrode with said control voltage to augment the gain variation.

\ 4. A method of controlling the gain oi a signal amplifierl tube provided with at least a cathode, signal control electrode and a signaloutput electrode, which includes the steps of applying signals to the control electrode, rectiiying low frequency alternating current to provide energizing voltage for at least said output electrode, rectifying said signals to provide a control voltage, automatically controlling said alternating current rectication with said control voltage thereby to vary the amplifier gain, deriving demodulated signals from the signal rectification, and utilizing said rectified alternating current to develop control voltage for preventing said derivation of demodulated signals. n

5. In a radio receiver provided with at least one modulated carrier wave transmission stage, said stage having a tube provided with at least a cathode, wave input electrode and a` cold electrode; the method which includes translating al- A ternating current into direct current for enervoltage the efciency of translation of said alternating current into direct current thereby to regulate the magnitude of said positive potential.

6. In a radio receiver provided with at least one modulated carrier wave transmission stage, said stage having a tube provided with at least a cathode, wave input electrode and a cold electrode; the method which includes rectifying an current potential for the cold electrode and a negative bias for the input electrode, rectifying received modulated carrier wave energy to provide a control voltage, and regulating in response to said control voltage said alternating current rectiiication thereby to regulate the input electrode bias value, and the magnitude of said positive potential. n

7. In a superheterodyne receiver embodying a converter tube, a localvoscillator tube and means for detecting the converted signal energy; the method including rectifying low frequency current to provide energizing direct current voltages for said converter and oscillator tubes, deriving from the detected signal energy a control i voltage, varying said rectification to 'control the magnitude of said energizing voltages, and varying the energization of at least said oscillator tube with said variable-.magnitude energizing direct current voltage in a sense to maintain the frequency of the converted signals substantially constant. e

8. In a wave transmission system including at least one electronic device provided with at least` an electron emission element, a cold output electrode and a cold control electrode; the method of regulating a characteristic of said device which from the energizing current, deriving a control voltage from transmitted waves, and regulating the magnitude of the energizingl current with said control voltage thereby to vary the value of the applied voltages.

9. In an electronic system having a plurality of e electron discharge devices and an energizing current supply network for providing energizing voltage for the respective electrodes of said devices; the-impr'ovement which comprises means for deriving a control voltage from electrical waves transmitted through the system, and means for regulating the magnitude of the energizing current flowing through the supply network in response to said control voltage thereby to vary said energizing voltage magnitude.

R LEE HOLLINGSWORTH. 

